The present invention relates to electrophoretic displays, especially encapsulated electrophoretic displays, and to systems for addressing such displays.
There are a number of interesting display media which provide good optical appearance, the ability to be easily constructed in large areas or on flexible substrates at low cost. Such display media include microencapsulated electrophoretic displays, rotating bichromal ball displays, suspended particle displays, and composites of liquid crystals with polymers, including polymer dispersed liquid crystals, polymer stabilized liquid crystals, and liquid crystal gels.
One drawback of such displays is that they are difficult to practically and economically address. One common means of addressing is known as direct drive addressing, in which each pixel is controlled by its own external drive circuit. This scheme is both expensive and impractical for displays containing a large number of pixels and for displays containing pixels that are tightly packed.
Another means of addressing is active matrix drive addressing, in which an electrically non-linear element is deposited on the display substrate. Examples of such electronically non-linear elements include transistors, diodes, and varistors. While this type of addressing is well-known and widely practiced, it is expensive to produce and difficult to achieve on plastic substrates.
A third means of addressing uses multiplexing, in which the conductive portions of the substrate are patterned so that rows of pixels on the substrate are electrically connected and columns of pixels on the substrate are also electrically connected. Typically, voltages are sequentially placed on the row electrodes, with the pixel data for each row being placed on the column electrode. This type of addressing is used for a variety of display media. Its use is limited, however, to displays in which the optical response as a function of applied voltage is non-linear and in which there is a significant voltage threshold to turn on the pixels. Display media which do not show a pronounced voltage threshold show poor contrast when driven with multiplex addressing drive schemes.
This invention provides electrophoretic displays, especially encapsulated electrophoretic displays, and systems for addressing display media of such displays. Systems of the invention allow for the addressing of display media that have poor threshold behavior without the high costs associated with using direct drive and active matrix drive addressing schemes. This is accomplished by using a multiplex addressing drive scheme in conjunction with a light system that generates a pattern of light.
There are numerous applications that can benefit from such a new addressing means. For instance, with the advent of information storing members (such as RAM and magnetic strips) in wallet-size card, it has become desirable to create xe2x80x98smart cardsxe2x80x99 capable of displaying on the card the updated information contained in the card. Typical cards such as credit cards have a magnetic strip on the rear surface, and a subset of the information contained on the magnetic strip, such as the cardholder name and card number, is embossed physically onto the front surface of the card. This usually suffices for this purpose, since the information on the strip is static. For transaction type cards, such as debit cards, however, there is a need for a means to display the information, which is stored on the card, as it is constantly changing. For example, phone cards and access cards may have certain value units which are purchased from some central or distributed authority. These value units (such as tokens, in the case of a subway, or phone minutes) may be actually stored locally on the card and interrogated offline, or the card may carry simply an identification number which is verified at each transaction and correlated with a central balance. The balance remaining on the card, however, is usually not indicated to the user. Prior art solutions to this problem involve systems such as that employed in the Washington D.C. subway, where a computer daisywheel printer prints the current balance on the card paper surface directly below the prior balance. There are several problems with this solution. First, the user can no longer simply swipe the card through a reader, but must insert it into a large machine in which the printer is housed. Second, cards made with this paper surface are not very durable, the information is not erased but basically crossed out; as a result, the card may be used only so many times before the balance space is filled up. Accordingly, such cards can benefit from the inclusion of a dynamic medium for updating the information contained thereon. Other examples of portable devices that can benefit from a novel system of updating the display on a card include access cards, smart cards, payment cards, price tags, and lottery tickets.
The present invention provides electrophoretic displays, especially encapsulated electrophoretic displays, and systems for addressing such displays. Displays of the invention include a photoconductive layer and an electrophoretic layer. Such displays may be rigid or flexible. Displays of the invention may also include a light image generated from a light source, a photoconductive layer, and an electrophoretic layer.
In one embodiment of the invention, a portable display card and system of updating the image on the card of the invention includes a light system that generates a light pattern, a card that includes a photoconductive layer and an electrophoretic layer. The photoconductive layer is adjacent the electrophoretic layer and the pattern of light reduces impedance in the photoconductive layer. The reduced impedance permits an applied electric field to address the electrophoretic layer. In some embodiments, the display cards also have one or more optical barrier layers.
The display cards have a front side and a rear side. When the rear side of the card is exposed to a pattern of light from the light source, light strikes the photoconductive layer and the photoconductive layer impedance decreases. The decreased impedance enables electrodes to apply a voltage, which addresses the electrophoretic layer, forming an updated image on the display card. In some embodiments, an electrode on the rear side of the card is clear. Light from the light source travels through the clear electrode to strike the photoconductive layer.
In another embodiment, the invention relates to an electrophoretic display including a light system, a photoconductive layer placed adjacent the organic, light-emitting layer, and an electrophoretic layer adjacent the photoconductive layer. Light from the organic, light-emitting layer strikes the photoconductive layer at a first point on a first side of the photoconductive layer, which faces the organic, light-emitting layer. A voltage is then generated at a second point on a second side of the photoconductive layer. This second point corresponds to the first point and faces the electrophoretic layer. The voltage at the second point addresses the electrophoretic layer at a predetermined point on the electrophoretic layer.
When the display is not illuminated, the impedance of the photoconductive layer is much greater than the impedance of the electrophoretic layer. The photoconductive layer therefore drops the majority of the applied voltage. When the photoconductive display is illuminated, the impedance of the photoconductive layer decreases, and the majority of the applied voltage then drops across the electrophoretic layer, forming an image. Specifically, the photoconductive layer is biased at a voltage on the xe2x80x9crearxe2x80x9d side, which faces the light source. The portions of the photoconductive layer that are exposed to light effectively transfer the voltage to the xe2x80x9cfrontxe2x80x9d side of the photoconductive layer, which faces the electrophoretic layer.
The present invention provides a display integrated into a smart card which is capable of being externally addressed. The display may be bistable, reflective, and preferably capable of being printed or laminated directly onto the card. It may be addressed directly by an electrostatic head.
In one embodiment, the invention incorporates features of a standard smart card. The embodiment may comprise a photoconductive layer, an electrophoretic layer, and an activation device all disposed in a substrate. In some embodiments, the activation device comprises a smart card interface and/or an electrophoretic layer interface. The smart card interface provides information to or triggers the encapsulated electrophoretic display to display a message. The smart card interface can be an information storage device, and the display can show information stored in the information storage device. The information storage device can have information associated with a subway access card, or financial information for a telephone card, a debit card, a credit card, or the like.
In another embodiment, an electrostatic head is embedded directly into the magnetic strip reader/writer. In this embodiment, the card""s magnetic strip is read in a single swipe and the display electrostatically addressed. In one embodiment, a laminate is constructed which consists of a rear conductive substrate (i.e., a photoconductive layer or a photoconductive layer and a first electrode), a layer of bistable electrostatically addressable ink material (i.e. an electrophoretic layer), and a protective top dielectric layer (i.e., a transparent layer). This structure is then laminated to a typical magnetic strip card, such as a subway access card. In one embodiment, the magnetic strip is laminated to the rear of the card. A section of a first electrode may be left exposed. When swiped in a specially designed reader, the magnetic strip reader can read the data on the card, write new data onto the strip, and on the opposite side of the card, an electrostatic head can write data onto the display material, making a single electrical connection to the first electrode and erasing and addressing the display material with positive and negative potentials relative to the first electrode. This hardware device which integrates a magnetic reader, writer, and electrostatic addressing head is also a novel construction. In some embodiments, the hardware device comprises a light source capable of updating the display by reducing impedance and providing an electric current, addressing the card. The magnetic reader can be used to sense the velocity of the swipe, and control the speed of the addressing. In one embodiment, magnetic strip and an electrophoretic layer interface are present on a card, the information read from and written to the magnetic strip preferably may not be visually displayed. Alternatively, the display may be integrated onto a standard smart card, which is then capable of being addressed externally when inserted into a reader.
In another aspect, the invention features a light system for addressing a smart card. The light system may comprise a light source incorporated in a standard smart card reader. The light system may comprise a light source, an activation device reader, an activation device writer, a display addressing head, a smart card connector and an electrophoretic connector. The electrophoretic display can be externally addressable. For example, the electrophoretic display may be addressable with an electrostatic head. In another embodiment, the electrophoretic display may be addressed by inserting the card into the light system that includes a standard smart card reader.
In another embodiment, the invention provides a method of updating an image on a card, for example, a smart card. The method comprises the steps of providing a card comprising an electrophoretic layer and a photoconductive layer. The photoconductive layer provides impedance and is adjacent the electrophoretic layer. The photoconducutive layer is exposed to a pattern of light. The light pattern decreases the impedance of the photoconductive layer and an electric field is applied, addressing the electrophoretic layer. In some embodiments, the pattern of light and resulting display on a smart card is responsive to display information present in the smart card interface. Methods of the invention can optionally include the steps of obtaining an output from an activation device of a smart card; and addressing an encapsulated electrophoretic display of the smart card to display information responsive to the output from the activation device. The invention may also further include a method of manufacturing a smart card. In one embodiment, the method comprises the steps of providing a photoconductive layer; disposing a magnetic strip on a surface of the photoconductive layer; and disposing an encapsulated electrophoretic display on a surface of the photoconductive layer.
Displays of the invention may also include a reflective substrate to direct light from the light system to the photoconductive layer. Displays of the invention may also include a dielectrophoretic layer, which is preferably fenestrated. Finally, displays of the invention may also include a capacitor.
In another embodiment of the invention, an emissive display includes an organic, light-emitting layer and a photoconductive layer disposed under the organic, light-emitting layer. In this embodiment, the organic, light-emitting layer is addressable at a first predetermined voltage. A first fraction of this first predetermined voltage drops across the organic, light-emitting layer, and a second fraction of this first predetermined voltage drops across the photoconductive layer. When the organic, light-emitting layer is addressed using this first predetermined voltage, it emits light, which strikes the photoconductive layer. This light causes the impedance of the photoconductive layer to decrease, so that the fraction of the first predetermined voltage dropping across the photoconductive layer is decreased and the fraction of the first predetermined voltage dropping across the organic, light-emitting layer is increased. The organic, light-emitting layer may then be addressed at a second predetermined voltage, which is lower than the first predetermined voltage. In an alternative embodiment, the emissive display includes a fenestrated dielectrophoretic layer, which modulates the amount of light striking the photoconductive layer.
The organic, light-emitting layer for use in displays of the invention includes an organic material disposed on a clear substrate. The clear substrate may be a glass, a plastic, or a polyester substrate, for example. The organic, light-emitting material may be an organic compound, an organometallic compound, an oligomer, or a polymer. Dispersed within the organic material may be inorganic semiconductors, such as CdSe conductors, for example.
The photoconductive layer for use in displays of the invention includes a photoconductive material, such as 2,4,7-trinitro-9-fluorenone complexed with poly(N-vinylcarbazole). The photoconductive material may be an organic photoconductive polymer, a dye-aggregate photoreceptor, or a pigment-based photoreceptor. In one embodiment, the photoconductive layer is disposed on a clear substrate, such as a glass, a plastic, or a polyester substrate, for example. In one embodiment, an optical barrier layer is disposed over or adjacent to the photoconductive layer. The optical barrier layer is a dispersion of opaque conductive particles in a polymer matrix, such as a dispersion of black pigment particles in an epoxy binder, for example. In other embodiments, the photoconductive layer includes a first photoconductive material and a second photoconductive material. The second photoconductive material is sensitive to a different variable of light than the first photoconductive material. The variable of light may be the wavelength of the light, the intensity of the light, or the duration of the light.
The electrophoretic layer for use in displays of the invention may be an encapsulated electrophoretic layer or a dielectrophoretic layer. An encapsulated electrophoretic layer of the invention includes a plurality of particles dispersed in a suspending fluid, which is encapsulated in a polymer matrix. The polymer matrix may include an aqueous polymer latex, such as a polyurethane, for example. The polymer matrix may be coated onto a substrate, such as a glass, plastic, or polyester substrate, for example.
In another embodiment of the invention, a display includes a clear top electrode. This clear top electrode may comprise a conductive material on a substrate. The clear top electrode may be indium tin oxide (ITO) coated onto a glass, plastic, or polyester substrate, for example.
The invention will be understood further upon consideration of the following drawings, description, and claims.